Oldsmobile 403 (Olds 403) Engine - Ask Anything

The Forgotten Olds 403Tim Campbell; Morristown, TN: Many people have the Olds 403 engine in their car and would like to upgrade. When you do the research on the Olds 403, you get a very broad range of opinions on the web ranging from "the blocks are no good" to "these engines can be made to produce some decent power." How about some help? Most of us would like to keep the Olds 403. With what you guys at Car Craft have done before with other oddball engines, we know you could build good horsepower and great torque. We are not talking about a race engine, but a true driver that is reliable-something you can beat on. We would love to hear that our engines have potential and that building them is worth it.

Jeff Smith: We called our Olds guy, Dick Miller at Dick Miller Racing (DMR), to get his input. He mentioned that even an average street Oldsmobile 403 would benefit from the typical improvements involving heads, intake, headers, and cam timing without having to go too deeply into the engine. We'll also assume that you would prefer to retain the stock torque converter and rear gear, which means being conservative with the cam timing. The stock Oldsmobile 403 enjoys the benefit of a giant 4.351-inch bore diameter with a relatively short 3.385-inch stroke. Miller says when Olds opened up the bore on these '70s-vintage engines, it intruded into the main webbing area requiring larger areas around the main webbing that weakens the crankcase. This isn't an issue with a mild street engine, but he recommends his five-cap halo-style main cap girdle for any Oldsmobile 403 motor that will see more than 6,000 rpm. The production Oldsmobile 403 also suffers from the typical late-'70s handicap of lame 8:1 compression by way of large, 83cc chambers.

One popular budget approach is to use 350 Olds heads to pump up the compression. Olds heads are identified by a large number cast into them. The 350 heads with a 5A casting offer a 68cc combustion chamber, the 6 head measures 70 cc, and the 7 head comes in at 69 cc. Miller says these 350 heads are the best, but there are still caveats. The universal problem with reviving old cast-iron heads is that by the time you've invested in new guides, a valve job, new stainless steel valves, filling the heat riser passage, and filling the depression between the center exhaust ports to prevent header leaks, you've got more money into a set of stock iron heads than the price of a pair of brand-new aluminum Edelbrock heads. DMR sells a set of Edelbrock aluminum Olds heads for $1,675, but keep in mind that these heads also require aftermarket aluminum roller rockers that will also pump up the price roughly another $250. The iron heads might be cheaper once they're rebuilt, but the flow probably won't be as good. Moreover, Edelbrock has revised the Olds head with improved flow, the combustion chamber is larger at 77 cc, but that will still gain some compression over the stock 83cc heads.

Assuming you will stick with a stock converter and gearing, Miller suggests a relatively mild hydraulic flat-tappet cam along the lines of a 219/233-degrees-at-0.050-tappet-lift cam with 0.476/0.508-inch lift and a lobe-separation angle of 110 degrees. This cam sells for $209 (PN 210-4) and will make some serious torque when combined with the Edelbrock Performer RPM intake you mentioned (PN 7111) and a set of 13/4-inch headers. All these parts taken as a whole represent a sizable investment, but you can do this a step at a time, spreading the cost out over a year or so, and still drive the car between mods.

L92 LS Head Swap
Josh Meyer; Sacramento, CA: I have a question regarding an article I found online about testing the new GM L92 cylinder heads called "550 hp for Under $4,900." If I want to reproduce the numbers posted in the article, all I need are L92 heads, a Comp Cams XR281HR cam, an 850-cfm carburetor and manifold, a stock bottom end, and the same headers? I'm very interested in the bottom end of the motor. Did you do anything to it to make this power?

2/8Even a stock cathedral-port head like this LQ4 317 cylinder head flows much better than the best early small-block Chevy head. Send your castings to West Coast Racing Cylinder Heads and have them put their CNC porting job to it; you'll have similar flow numbers to the L92 head with far better velocity and more usable torque.

Jeff Smith: The story you are referring to ran in the May '07 issue where we used a stock, 6.0L short-block to make this power. The engine did make 551 hp at 6,800 rpm using the more aggressive Comp Cams XR281 you mentioned. The baseline test for the story included a GM Performance Parts Hot cam with specs of 219/228 degrees of duration at 0.050 tappet lift and 0.525-inch valve lift for both the intake and exhaust using the stock 1.7:1 rocker ratio. There was also a slight error in the story when it originally ran that a couple of readers noticed. In the story, we claimed that the engine was a base, iron-block LQ4, because that's what we thought we had. But in the photo in which we show checking valve-to-piston clearance, a reader caught flat-top pistons that are actually used on the higher-compression LQ9 engine. The LQ4 engines are rated at 9.4:1 with a dished piston, while the LQ9 engines enjoy 10.0:1 compression using a flat-top piston, which means we actually had the better LQ9. We completely missed that little clue because we were focused on making sure the valves didn't hit the pistons. The difference in compression is roughly a half point, which is worth less than 2 percent power. Even at 550 hp, that's worth 5 to 7 hp. The original baseline with the stock LQ9 cam certainly benefited from this additional compression, making 439 lb-ft of torque at 4,400 rpm and 425 hp at 5,600 rpm.

While the long-block was stock LQ9, it also enjoyed a large, single-plane, GM Performance Parts intake, a Holley 750-cfm carburetor, and a pair of Kooks 1 3/4-inch headers feeding a pair of 2 1/2-inch Flowmaster mufflers. Next, we added the GMPP Hot cam and the engine improved to 450 lb-ft of torque at 5,000 rpm and 483 hp at 6,000 rpm. That is incredibly impressive given the stock LQ9 cathedral-port heads. The test also included a set of LS6 valvesprings that came with the Hot cam kit. These initial dyno tests were outlined in the Apr. '07 issue of Car Craft. To run these LS engines with a carburetor, you will also need an MSD PN 6010 LS6 spark box that allows you to create your own spark curve to operate the factory distributorless ignition system (DIS).

3/8<strong>CC Quickies</strong><br />
In the story on Thomas Moore's shop, one of the more interesting backstories is that he disassembled and removed the 1928 Rotary Lift hydraulic hoist out of the ground (a 9-foot deep pit), welded up the pinhole leaks, and then welded a new outer casing around the original cylinder! That's Thomas welding with son Cameron looking on.

The second installment in the May issue pushed the power from 483 hp at 6,000 rpm to 551 hp at 6,800 rpm with the addition of both the larger, rectangle-port L92 castings, a Comp XR281 cam (228/230 degrees of duration at 0.050 with 0.571/0.573-inch lift and a 112 degree LSA), and an 850-cfm Holley carb. While this is impressive horsepower, you are smart to ask about the short-block because at 6,800 rpm, those cast-aluminum pistons quickly become an endangered species. Higher rpm imparts more stress on cast pistons and those stock rod bolts. The question is not whether a piston will crack, but rather how much damage will occur when it does. For durability with this larger camshaft, you will need to add a set of forged pistons, aftermarket rods, and a good torque-plate-honing job. The cast crank should be fine for street use even up to 6,800 rpm.

There is a larger question, however, that should be addressed. In the original story, the swap to the rectangle-port heads and big cam sacrificed mucho torque below 4,800 rpm. Add to this that the engine's power band (the rpm between peak torque and peak horsepower) has now migrated to between 5,400 and 6,800 rpm. That means the engine's power curve doesn't start until 5,400 rpm. To take full advantage of all that power, you also must shift the engine at 7,000 rpm or higher. The reason the L92 heads are so attractive is that you can purchase a pair of brand-new heads and the necessary offset intake rocker arms for around $1,100. The heads we tested were from Scoggin-Dickey Parts Center, priced at $899.90 a pair while the rocker arms and valvetrain parts are another $225. While these parts make excellent peak horsepower, the combination sacrifices midrange torque to get there.

An alternative idea is to port the original cathedral heads to improve the airflow while maintaining the higher port velocity of the smaller cross-section port area. A milder cam will put the peak horsepower rpm at 6,000 (rather than almost 7,000), and the peak torque will also drop down to a more useful 4,500 rpm. Why would we want to do this? To better illustrate the idea, I plugged the 551hp power curve into the Quarter Pro dragstrip simulation program using a 3,600-pound street car with a 3.55:1 rear gear and a 2,800-rpm converter. The program estimated the run at an 11.52-at-114.9-mph pass shifting at 7,000 rpm. Next, I increased the torque by 22 lb-ft between 3,000 and 5,000 rpm and reduced the peak horsepower by 30 hp to 520 at 6,000 rpm. While most enthusiasts might think that losing 30 hp would guarantee a slower run, the Quarter program generated a quicker and faster 11.42-at-115.3 mph. This occurred because the added torque in the middle helped accelerate the car more efficiently with the car's street-oriented 3.55:1 gear and mild stall speed. Conversely, if you had a drag-race-only car with a much deeper rear gear and perhaps a four- or five-speed, close-ratio manual trans, then that big head/big cam package would take advantage of the higher power band and run quicker.

The bottom line here is that you could spend roughly the same amount of money to have a stock set of cathedral heads CNC ported and match them to a milder camshaft and you would have an engine that makes great power and is very tractable on the street. This milder package won't make heroic horsepower numbers, but if your goal is quicker acceleration rather than just bragging rights at the next bench racing session, then the more conservative approach just might be the way to go. As an example, West Coast Racing Cylinder Heads offers a Stage 2 CNC porting operation for the stock LQ4/LQ9 317 cathedral-port heads that will flow virtually the same numbers at the midlift up through 0.500-inch lift as the L92 heads while delivering far superior port velocity. Plus, WCRCH will port your supplied castings for $1,375, which is only a few bucks more than the price of the new L92 heads and valvetrain. The WCRCH heads come with new 2.02/1.57-inch stainless valves and Patriot springs. The cathedral heads will tend to run better with a shorter cam similar to a Comp XR269HR (216/220 at 0.050 with 0.525/0.532-inch lift and a 114 degree lobe-separation angle). This will make a bunch of torque in the usable rpm range for a street engine compared with the larger 281 cam. The thundering herd is infatuated with L92/LS3 heads right now because those big-port heads offer sewer pipe flow numbers. But for a mild street engine, I believe the more conservative cathedral-port heads are a smarter choice.

Better Living Through Chemistry
Mark LeBlanc; New Orleans, LA: I really enjoy reading your magazine. It has helped me with my projects. I am looking for the product I read about a few months ago. I think it was about reworking a console. It was a resin-impregnated cloth that you could form and then it hardened when exposed to sunlight (UV rays). I want to use it on the wing for my Vette. I appreciate any help you can give me.

4/8The twill weave is very easy to work with, cuts with sharp shears, and can be completely hand-formable. Plop it outside in the sun for a few minutes and you're good to go.

Jeff Smith: The material you're looking for is called HyperFiber, sold by Percy's High Performance. This is a fiber-weave material similar to fiberglass or even carbon fiber. If you've ever worked with fiberglass, you know that mixing the resin with the layers of fiberglass is a messy proposition and difficult for a rookie to do correctly. The beauty of the HyperFiber is that the resin is mixed in the proper ratio with the cloth and then covered with a dry film on both sides of the fiber so no mixing is necessary and your fingers don't get all sticky. Curing the final product is even easier. The trick is to work with this stuff inside, away from direct sunlight. The fiber is easily malleable by hand to create the desired shape. Once the final shape is achieved, simply move the HyperFiber into direct sunlight. The ultraviolet (UV) component in sunlight will cure the resin and within a few minutes, the part will have hardened into your final piece. We played with this stuff at the recent PRI show in Orlando, Florida, and it works exactly as they say. Once formed, the HyperFiber can be drilled, sanded, painted, and ready for use. Percy's says that HyperFiber is impervious to engine heat (although probably not exhaust temperatures), so this product could be used for engine covers or maybe even a cool intake duct! Of course, ease of work and application mean this stuff is a little more expensive than fiberglass. A 12x21-inch sheet of pre-impregnated, HyperFiber wire-reinforced (which is a little stiffer) twill weave is $271.17, but Percy's offers all kinds of different sizes and applications. Some of the more interesting ones are a trans tunnel kit ($347.38) and a mini-tub kit for $748.10. Percy's even offers a trunk pan kit for $529.10. The company also sells the HyperFiber twill weave material dry, and you then mix the resin with the weave as you would with fiberglass. This is slightly less expensive than the integrated material but will require more skill. The same size dry twill weave cloth costs $204.33, and then you must add the resin. You can order any of these parts directly from Percy's on the website.

Hot Trans AmEric F. Marx; Racine, WI: I have two problems relating to my LT1 '95 Trans Am Firebird. First, the low coolant sensor is located somewhere under the hood. It seems the expensive GM service manuals specifically for this vehicle do not tell a person where this sensor is located. I emailed Pontiac with my question, and you may be surprised to learn that they wrote me back and said that they don't know where it is either. Can you guys tell me where I might find this sensor on the car?

Also, I do not like the way the engine coolant fans are triggered by the ECM. The ECM tells the two dual-speed electric fans to come on at low speed when engine temperature reaches 226 degrees, and that high speed occurs at 235 degrees. This annoys me to no end watching my temperature gauge climb to the far end of the scale before the fans start. It would seem to me that they should start at around 200 degrees and shut down somewhere around 195 degrees. I have never seen a car that has a cooling system set up like this. On every other car I have owned, the temperature gauge moves very minimally and the fans cycle quite frequently. Do you know of any way the ECM can be adjusted to modify these settings? It makes me nervous having it operate this way, as I don't think is very good for the aluminum heads that are on this engine either.

5/8<strong>CC Quickies</strong><br />
AFR has just released a brand-new composite intake manifold for the small-block Chevy, a two-piece design. There is a dual-plane, a short single-plane, and a tall single-plane. We've been privy to AFR's dyno testing. One test we saw hit 533 hp on an AFR-headed small-block.

Jeff Smith: We did a little digging and it appears that the low-coolant sensor on your car is located on the passenger side of the radiator tank. It is difficult to see and you may need to remove the battery to access the sensor.

Apparently the sensor is tied only to the light on the dash, so it does not contribute to illuminating the check engine light. It also is somewhat troublesome, and corrosion or debris in the cooling system may arbitrarily trigger the light. So if you want, you can merely unhook the connection and go back to manually checking the cooling system level.

As for your engine temperature concerns, it first sounded like the gauge you were using may not be accurate (which is a common problem, especially with factory gauges), but looking into the factory fan settings, it appears these high temperatures were intentional. The first coolant-fan-switch temperatures we found were in a Hypertech instruction manual that indicated the factory ECU triggers the fans full on at 240 degrees F and turns them back off at 225 degrees F. That's a bit warm for a typical summer day that could easily kick your under-hood temperatures well over 240 degrees F. The Hypertech Power Programmer III that we looked at has the capability, among other things, to reprogram the electric fans to kick on at two different temperatures depending on your choice of thermostats. With the 180-degree Hypertech thermostat, the fans will kick on at 213 degrees and shut down when the engine temperature falls to 205 degrees. Or, you can opt for the 160-degree thermostat, and the programmer will trigger the fans to come on at 192 degrees and shut off at 185. This second option seems to be the most ideal as it will keep your engine operating somewhere around the 190-degree mark.

The reason the factory intended these engines to run so hot was strictly to satisfy emissions demands. Higher engine operating temperatures reduces hydrocarbon emissions, but it's certainly not the ideal situation for making power. Higher coolant temperature also increases the intake manifold and cylinder head intake port temperature. This heats the incoming air and fuel, which may improve mixture vaporization, but more important, it heats the air, making it less dense. This makes less power and also makes the engine more prone to detonation. The only snag we see with the Hypertech Power Programmer III, (PN 345752) is its $399.95 price, which seems a bit steep just to change the fan temps. The programmer can also allow you to change the rev limiter, speedometer calibration, and shift firmness and timing along with a slight change in timing and air/fuel ratio to produce a little more power, but you didn't mention those items. Jet also makes a similar GM programmer that offers the same features plus it shows a slight gain in power with some additional tuning. The Jet Stage 2 Power Control Module is PN 19614S and sells for $329.95

We also spoke to Mark McPhail, an ex-GM engineer who has worked with us on many Car Craft projects and who now does aftermarket ECU programming and tuning. You can contact him about doing a simple reprogram of your ECU that will trigger the fans at the exact temperature you want for much less than $400. Plus, McPhail might also be able to pull a few other reprogramming ideas out of his electronic bag of tricks if there is something specific you need. Regardless of which option you choose, the engine should make a little more power just by running about 40 degrees cooler!

Ford Motor Swap
John Spiess via CarCraft.com: I have a complete wrecked '05 P71 Crown Vic. I want to swap the front suspension, engine, trans, and rearend into a '75 Ford F-100 pickup. The fabrication work on the suspension is no problem, but what difficulties will I run into with the wiring and PCM? I have the complete car. Does anyone make a stand-alone harness that will work? I want to use the factory stuff for reliability and economy. Any information would be greatly appreciated.

6/8The Detail Zone custom harness package includes the Telorvik system that includes a custom panel where all the sensor and control wiring connects. This panel also plugs directly to the factory Ford computer. It's a slick system that allows individual wiring of each pin to the computer without having to wrestle with obscure factory wiring connectors.

Jeff Smith: We did a little searching and came across custom wiring harness conversions for two-valve Ford mod motors at Ron Francis Wiring. The company makes conversions for all the Ford mod motors up until 2004-of course, right? In '05, Ford converted to electronic throttle. We spoke to Scott Bowers, owner of Ron Francis Wire Works and the Detail Zone, who told us that they've been working on '05-and-later aftermarket harnesses, but the complexity of Ford's new system has made this a time-consuming effort. For the '04-and-older two-valve Ford mod motors, Bowers' system is a little different from most. He creates a box that allows you to individually wire in each separate sensor or control wire for the engine. The box also incorporates necessary fuses, relays, and other connectors and then the stock Ford computer plugs in to that box. This makes wiring the individual sensors much easier, and then you can route and bundle the wires in a way that best fits your vehicle.

I asked Bowers about retrofitting the '05-and-newer two-valve mod motors with an '04-or-earlier computer and running the engine with a cable-operated throttle. Bowers says he has successfully accomplished that conversion for a manual transmission-equipped system, but, again unfortunately for you, the '05-and-later automatic applications are far more complex because the new automatic transmission does not play nicely with the older electronics. So that idea is also not going to work. This leaves one of two choices for your truck, John. The first is to use the existing Ford OE wiring harness and computer. Bowers says the Detail Zone can work with you to do any necessary tuning and also disable the OE Passive Anti-Theft System (PATS) that is integrated into all the later-model computers. The other option is to sell the '05 engine and find an '04-or-earlier version, but frankly that's probably not going to happen. So it appears you may be stuck with the stock factory harness. It's tedious work, but you can extend the length of the harness if necessary to allow you to place the computer where you desire. If this is the plan, work slowly, do one wire at a time, and remember that each connection will need to be crimped using non-insulated butt connectors and then protected with shrink-wrap. You might also consider alternating the position of where you make these connections so as not to create a large bulge in the harness from all the butt connectors.

For others who may consider swapping a mod motor, Bowers suggests knowing exactly which engine you have (or are about to buy) so that ordering the correct harness will be less stressful. According to Bowers, Ford used two types of fuel injectors on the mod motors. The early EV-1 injector uses a rectangular wire harness plug, while the subsequent EV-2 injector employs a smaller, oval wire plug. The next biggest issue is deciding upon the fuel delivery system you want to use. The factory mod motors employed a single fuel line from the tank to the engine. While this can be retained, Bowers says the factory pump is difficult to adapt to earlier fuel tanks, and that can easily drive up the cost of the conversion. The alternative is to build a return-style fuel system using a vacuum-modulated mechanical fuel pressure regulator that can alter the fuel pressure based on engine load. The Detail Zone instructions call for an idle fuel pressure slightly lower than the 43 psi needed at WOT.

Performance Gas Cap
Vince Terrana; Bradenton, FL: A couple of years ago I was looking for a motor for my daily driver. A friend had a 350 Chevy ready to be assembled but never did. I bought the basket case and put it together. When first built it had a Magnum 280 cam, a Performer dual-plane, headers, a Holley 650 vacuum-secondary carb, an HEI with an ignition box, stock heads, and a 2,000-rpm stall convertor. I installed the motor in an '83 G-Body Olds wagon. I was not impressed with the performance and realized it had too much cam. First, I put in a set of Rhoads lifters but still was not happy, so I changed to a Comp 268. Still not much change; this car could not spin the tires. The Holley carb was new, but I changed to a Quadrajet. That felt a little better but not much. I played with timing, different plugs, whatever I could think of with no change. I vented the tank by modifying the gas cap by removing the restrictors and drilling a hole in it. I also left the vent line uncapped. I'm running a stock mechanical fuel pump with no return. Recently, after a gas stop, I left my gas cap behind and that created the biggest performance increase ever-it's a different car now. My question is-what happened?

7/8When we built the fuel system for our LS-powered Orange Peel Chevelle, we added a 1/2-inch vent line to the tank that supplemented the stock 5/16-inch line. We used a brass fitting that Tim Moore brazed into our tank.

Jeff Smith: Sometimes the simplest solutions are the best. From your description, it sounds like a simple case of insufficient venting. This is not an unusual situation. It is much like trying to pour liquid out of a closed container with no vent. I have one of those 5-gallon plastic fuel cans on which the vent hole has not been opened because when fuel is stored in the can, I don't want it to vent. This is the one I use to store fuel, but every once in a while I try to use it to pour gas into one of the cars. With one of those 1-inch hoses on the end of the jug, it takes forever to pour fuel into the car because there's no vent. Use a jug with a vent and the fuel shoots into the tank in seconds.

Your gas tank works the same way. Combine a high-output engine that has greater fuel requirements with a too-small vent and the result is that insufficient fuel will reach the carburetor. Mechanical fuel pumps don't really "pull" fuel toward the carburetor. These pumps operate by creating a low pressure area in the fuel line and tank. Higher atmospheric pressure pushes on the fuel in the tank, moving the fuel toward the engine. The greater the pressure difference between the fuel pump and the atmospheric pressure in the tank, the more fuel moves. With a restricted vent, atmospheric pressure drops inside the tank and to no one's surprise, the fuel moves more slowly. So figure out the best way to increase the vent size on your tank and you will be good to go!

8/8<strong>CC Quickies</strong>
<br />
We've been on the dyno plenty in the past 30 days. Here's another teaser. This is Vortech's latest carbureted blow-through hat bolted on a 6.0L LS2 with L92 heads, an LS7 camshaft, and a Vortech V3 S-Trim self-contained supercharger driven by a very cool March Performance six-rib accessory drive. At only 6 psi, this motor made 617 hp on pump gas and is capable of much more. We'll have more on this soon.